The rapid development of semiconductor technology both in terms of unique and different devices and in higher packing density has led to unique requirements for materials and device structures. Typical examples are the use of better passivating materials, better insulating materials, unique optical materials, etc.
A particularly interesting type of structure is that involving alternating layers of single-crystal insulator and semiconductor. Such a structure has a number of potentially interesting characteristics associated with the single crystal nature of the various layers including tunneling between layers, low trap density, etc.
In many semiconductor structures, minimization of the number of defect states (the trap density) in the interface between two different materials (e.g., between semiconductor and insulator in a metal-insulator-semiconductor structure) is highly desirable. This leads to much better device performance. To minimize trap density, it is desirable to have not only a single crystal layer of insulator lattice matched to the semiconductor but also a crystal structure closely compatible to the semiconductor. In this way, the discontinuity at the insulator-semiconductor interface is minimized so the trap density is minimized.
A number of references have been concerned with epitaxial dielectric layers on various semiconductor surfaces. Particularly interesting are two articles, the first entitled, "Insulating Epitaxial Films of BaF.sub.2, CaF.sub.2 and Ba.sub.x Ca.sub.1-x F.sub.2 Grown by MBE on In? Substrates" by P. W. Sullivan et al, Journal of Crystal Growth, pages 403-413 (1982) and a second entitled, "MBE-Grown Fluoride Films: A New Class of Epitaxial Dielectrics" by R. F. C. Farrow et al, Journal of Vacuum Science and Technology, 19(3), pages 415-420 (September-October 1981). Also of interest is an abstract by C. Fontaine, S. Siskos and A. Munoz-Munoz entitled, "Epitaxial Growth of Lattice Matched Group II Fluorides on GaAs Substrates" appearing in the abstracts for the Second European Workshop on Molecular Beam Epitaxy, Sussex University, Brighton (Mar. 27-30, 1983).